1. Field of the Invention
The present invention relates to a torque measuring device for a rotating body, which is to measure a torque of a rotating body without getting in touch with its rotating portion.
2. Description of the Related Art
A torque measuring device for a rotating body (hereinafter, referred to simply as “torque measuring device” as appropriate) is set between a driving shaft powered and a driven shaft loaded, and measures a rotating torque in a non-contact manner. Such a torque measuring device is disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-22566, which is used, for example, to measure a rotating torque between a measurement roller and a brake system in a chassis dynamo rotated by a wheel of a vehicle.
FIG. 1 is a front view of a conventional torque measuring device 50, and FIG. 2 is a side view (partly cut away and sectioned) of the torque measuring device 50 of FIG. 1. As shown in FIGS. 1 and 2, the conventional torque measuring device 50 includes: a rotary section 51 rotatably disposed between a driving shaft 91 powered and a driven shaft 93 loaded; and a stationary section 55 fixedly disposed so as to surround the rotary section 51. The rotary section 51 integrally includes: a first flange 52 to be fixedly jointed to a driving shaft flange 92 of the driving shaft 91; a second flange 54 to be fixedly jointed to a driven shaft flange 94 of the driven shaft 93; and a hollow cylinder 53 having a hollow 59, and having the first and second flanges 52 and 54 formed respectively on both edges thereof. The stationary section 55 includes: an annulus 56 located so as to surround the second flange 54; and a chassis 57 to which the annulus 56 is fixedly attached via attaching members 58.
A primary coil 87 is provided at the inner circumference of the annulus 56 disposed outside the second flange 54, and a secondary coil 88 is provided at the outer circumference of the second flange 54. The primary and secondary coils 87 and 88 in combination constitute a rotary transformer 89, thereby supplying electric power to the rotary section 51.
Torque detectors 61 as strain gauges are provided at the inner circumference of the hollow cylinder 53, a plurality of light emitting elements 67a to 67n, which are adapted to emit light according to an output from each of the torque detectors 61 thereby outputting an optical signal, are provided at the outer circumference of the second flange 54 so as to be arrayed along the secondary coil 88, a light receiving fiber 71 for receiving the optical signal from the light emitting elements 67a to 67n is provided along the primary coil 87 on the inner circumference of the annulus 56, and optical-electrical signal converters (not shown) for converting the optical signal into an electrical signal are provided at the ends of the light receiving fiber 71.
In the torque measuring device 50, when the driving shaft 91 rotates, the output from each of the torque detectors 61 is carried via the light emitting elements 67a to 67n and the light receiving fiber 71 to the optical-electrical signal converters (not shown) and is thereby detected, thus measuring a rotating torque.
As described above, the torque measuring device 50 is set between the driving shaft 91 and the driven shaft 93 and is adapted to measure a rotating torque in a non-contact manner. The torque measuring device 50, however, has the disadvantage that due to provision of the multiple emitting elements 67a to 67n, a large amount of electricity is required for the aerial power supply operation by the rotary transformer 89 constituted by the primary and secondary coils 87 and 88, and therefore the number of the coils must be increased thus increasing the burden at the electric circuit.
Also, due to the influence of variation resulting from the inter-individual variability of the plurality of light emitting elements 67a to 67n, such as difference in light amount, directivity characteristic, and the like, the crest value of the optical signal received at the stationary section 51 is varied causing adverse effects on the electrical property.
And, the light emitting elements 67a to 67n are provided at the outer circumference of the rotary section 51 and therefore suffer a large centrifugal effect due to the rotation of the rotary section 51. When the rotary section 51 rotates at a high speed, the light emitting elements 67a to 67n can be damaged resulting in deterioration of reliability.